when i turn on, Philliips TV is not on

[Nish]

Re: when i turn on, Philliips TV is not on

What are the voltages on IC951? something is wrong in that circuit, that is why there is no regulation happening. Maybe shorted C955,C954? I guess it might be PC901? if you don't have one try exchanging PC902 with PC901.

IC951= 6.60v I use ground of C951A

I un solder PC901 now I measure that pads. Still same voltage.

I replace PC902 with 817A optocoupler. Still same voltage.

How can I check if C955,C954 are shorted. Can I lift one pad of cap?

[R_J]

Re: when i turn on, Philliips TV is not on

IC951= 6.60v I use ground of C951A

I un solder PC901 now I measure that pads. Still same voltage.

I replace PC902 with 817A optocoupler. Still same voltage.

How can I check if C955,C954 are shorted. Can I lift one pad of cap?

Just check C955/954 in circuit.

[R_J]

Re: when i turn on, Philliips TV is not on

What are the voltages on IC951?

[Nish]

Re: when i turn on, Philliips TV is not on

What are the voltages on IC951?

IC951 all 3 pin has 6.60v. But cathode is GND.

I check both end of cap is 6.60v

Using ground of C951A

[R_J]

Re: when i turn on, Philliips TV is not on

IC951= 6.60v I use ground of C951A

I un solder PC901 now I measure that pads. Still same voltage.

I replace PC902 with 817A optocoupler. Still same voltage.

How can I check if C955,C954 are shorted. Can I lift one pad of cap?

You needed to replace PC901 NOT pc902 I only suggested exchanging them if you did not HAVE ONE.

[R_J]

Re: when i turn on, Philliips TV is not on

IC951 all 3 pin has 6.60v. But cathode is GND.

I check both end of cap is 6.60v

Using ground of C951A

Install a TEMPORARY jumper wire in J14, as the power supply board does NOT connect the negative side of C951A/B to the negative of IC951. WITHOUT this connection, the power supply standby 5 volts has no reference.
I suspect that the two points only get connected whn the main board is connected, something only Philips would do.
The grounds I marked in Blue, DO NOT connect to the grounds I marked in Green, this is why the supply has no reference and why the output is too high. Installing the J14 jumper should result in a stable +5 volts.

[Nish]

Re: when i turn on, Philliips TV is not on

You needed to replace PC901 NOT pc902 I only suggested exchanging them if you did not HAVE ONE.

Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?

[R_J]

Re: when i turn on, Philliips TV is not on

Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?

Had you told me the voltages on IC951 earlier, I would not have suggested the capacitorsT he caps will be ok, Install the jumper wire I suggest this will fix this issue.

[Nish]

Re: when i turn on, Philliips TV is not on

You needed to replace PC901 NOT pc902 I only suggested exchanging them if you did not HAVE ONE.

Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?

[R_J]

Re: when i turn on, Philliips TV is not on

Sorry I miss type. I replaced PC901. By the way I will replace c954. But value is 0.1, is that uF or nF?

Why??? Just put the original one back in. THEN add the jumper Like I suggested. Look at the schematic... then check the resistance between C951 ground and ic951 ground. If the grounds are not connected together how can it work?
The cap is likely .1µf

[Nish]

Re: when i turn on, Philliips TV is not on

Had you told me the voltages on IC951 earlier, I would not have suggested the capacitorsT he caps will be ok, Install the jumper wire I suggest this will fix this issue.

I am outside now, I will do the jumper and update later. Thanks

[Nish]

Re: when i turn on, Philliips TV is not on

Install a TEMPORARY jumper wire in J14, as the power supply board does NOT connect the negative side of C951A/B to the negative of IC951. WITHOUT this connection, the power supply standby 5 volts has no reference.
I suspect that the two points only get connected whn the main board is connected, something only Philips would do.
The grounds I marked in Blue, DO NOT connect to the grounds I marked in Green, this is why the supply has no reference and why the output is too high. Installing the J14 jumper should result in a stable +5 volts.

I install jumper at J14. The C951A ground and IC951 ground are connected together. Now I have IC901 cathode is 6.60v and ref is 1.4v. PC901 still pin 1 and 2 are 6.20v.

I checked around IC951
R955 = 1.4v
C955 = 1.4v (which is connected to ref of IC901)
C954 = 1.4v (which is connected to ref of IC901)

ZD907 = -5v

[Nish]

Re: when i turn on, Philliips TV is not on

Why??? Just put the original one back in. THEN add the jumper Like I suggested. Look at the schematic... then check the resistance between C951 ground and ic951 ground. If the grounds are not connected together how can it work?
The cap is likely .1µf

Yes I put back the original one

[Nish]

Re: when i turn on, Philliips TV is not on

Is there anything I can do further with this board?

[R_J]

Re: when i turn on, Philliips TV is not on

Is there anything I can do further with this board?

Did you ever replace C951? The feedback circuit is very simple I don't know what could be causing it not to work, Have you checked that all the resistors have the correct resistance, even R952.
R954 and R955 set the voltage for the reference pin on ic951. If the voltage on C951A is too high (or has too much ripple) IC951 should start to conduct and lower the voltage on PC901 pin2, this lights the led in PC901 telling ic901 to lower the voltage, this is how it regulates.
As you can see, if the feedback is not working, IC901 operates full, and the result is too high a voltage on ZD951/C951A. If it was'nt for ZD951 (6.2v zener) clamping that voltage it could be 10 volts or more.
The problem is in that feedback circuit.

[Nish]

Re: when i turn on, Philliips TV is not on

Did you ever replace C951? The feedback circuit is very simple I don't know what could be causing it not to work, Have you checked that all the resistors have the correct resistance, even R952.
R954 and R955 set the voltage for the reference pin on ic951. If the voltage on C951A is too high (or has too much ripple) IC951 should start to conduct and lower the voltage on PC901 pin2, this lights the led in PC901 telling ic901 to lower the voltage, this is how it regulates.
As you can see, if the feedback is not working, IC901 operates full, and the result is too high a voltage on ZD951/C951A. If it was'nt for ZD951 (6.2v zener) clamping that voltage it could be 10 volts or more.
The problem is in that feedback circuit.

Sorry, I didn't have internet for 3 days....
No I didn't replace C951.
R952 = 1.991k
R954 = 6.01k
R955 = 2.951k
"*set the voltage for the reference pin on ic951." Am I using external power supply at what voltage, while the board plug in the outlet? I am confused

[R_J]

Re: when i turn on, Philliips TV is not on

What I said was that R954 and R955 set the voltage for the reference pin on ic951, thats how the those reference ic's work. R954 and R955 form a voltage divider, So when the voltage on the top of R954 increases, the voltage on the other end of R954 increases, this will cause IC951 to turn a bit more lowering the voltage on PC901 pin 2.
But this is not happening so the led in PC901 never turns on.

[Nish]

Re: when i turn on, Philliips TV is not on

I have replaced R954. Now the voltage attached images.
Across ZD907 = -3.0v
Across C906 = 16.20 solid
Across C912 = 11.21 solid
Across C951A =5.38

[R_J]

Re: when i turn on, Philliips TV is not on

That looks like it is working ok. Now check the voltage across C906 to see what it reads. To turn on the rest of the power supply you would need to connect P-ON-N1 to AL+5V

[Nish]

Re: when i turn on, Philliips TV is not on

Across C906 = 16.20 solid